Torque motor having uniform torque output characteristics

Abstract

A torque motor comprises a rotor having a pair of permanent magnet groups, and a pair of stator cores. Each magnet group includes a plurality of plate or rod-shaped permanent magnets arranged in a circumferential direction. The magnet groups are arranged asymmetrically with respect to a rotary axis of the rotor. That is, one magnet group is displaced one-half angle of the pitch angle of each permanent magnet from the symmetric position of the other magnet group with respect to the rotary axis of the rotor. Alternatively, the stator cores are arranged asymmetrically with respect to the rotary axis of the rotor so that a front end of one stator core is displaced from the symmetric position of a front end of the other stator core in the circumferential direction. A cylindrical magnetic cover is fitted on the rotor to cover the permanent magnets circumferentially.

What is claimed is:  
     
       1. A motor comprising: 
       a rotor having a pair of magnet groups thereon for providing a pair of magnetic poles respectively around a rotary axis thereof, each of the magnet groups including a plurality of permanent magnets arranged in a circumferential direction;  
       a solenoid unit; and  
       a stator coupled with the solenoid unit for providing a pair of magnetic poles which face the magnetic poles of the rotor when the solenoid unit is energized, the magnetic poles of the stator having respective front ends that the magnet groups approach first during rotation of the rotor,  
       wherein one of (1) the front ends of the stator and (2) the magnet groups are arranged asymmetrically with respect to the rotary axis of the rotor, whereby the front ends of the stator are asymmetrical relative to the magnets of the rotor with respect to the axis of rotation, thereby to reduce periodic fluctuations in generated torque arising from said front ends during rotation of the rotor, wherein one of the magnet groups is displaced in the circumferential direction from a diametrical line crossing the rotary axis of the rotor and a circumferential center of the other of the magnet groups.  
     
     
       2. A motor as in claim  1 , wherein each of the permanent magnets is in one of a plate and rod shape in section. 
     
     
       3. A motor as in claim  1 , wherein one of the front ends of the stator is displaced in the circumferential direction from a diametrical line crossing the rotary axis of the rotor and the other of the front ends of the stator. 
     
     
       4. A motor as in claim  1 , wherein the permanent magnets in each of the magnet groups are separated from each other in the circumferential direction. 
     
     
       5. A motor as in claim  4 , wherein a non-magnetic material is filled in the spaces between said permanent magnets in each of the magnet groups and an outer periphery of the magnet groups is molded with a resin material mixed with fine magnetic particles. 
     
     
       6. A motor as in claim  1 , wherein the rotor has a magnetic member covering the magnet groups. 
     
     
       7. A motor as in claim  6 , wherein the magnetic member is in a cylindrical shape. 
     
     
       8. A motor as in claim  6 , wherein the magnet groups are separated from each other in the circumferential direction leaving spaces therebetween, and the magnetic member has non-magnetic parts which cover the spaces, wherein said non-magnetic parts comprise slits in the magnetic member. 
     
     
       9. A motor as in claim  6 , wherein the magnetic member and the permanent magnets have a substantially uniform gap therebetween in the circumferential direction. 
     
     
       10. A motor as in claim  1 , wherein the asymmetric arrangement corresponds to half a pitch of one of said permanent magnet. 
     
     
       11. A motor as in claim  1 , wherein a diametrical line crossing the rotary axis of the rotor and one of the front ends of the stator crosses the other of the front ends of the stator. 
     
     
       12. A motor comprising: 
       a rotor having a pair of magnet groups thereon for providing a pair of magnetic poles respectively around a rotary axis thereof, each of the magnet groups including a plurality of permanent magnets arranged in a circumferential direction;  
       a solenoid unit; and  
       a stator coupled with the solenoid unit for providing a pair of magnetic poles which face the magnetic poles of the rotor when the solenoid unit is energized, the magnetic poles of the stator having respective font ends that the magnet groups approach first during rotation of the rotor,  
       wherein one of the front ends of the stator and the magnet groups are arranged asymmetrically with respect to the rotary axis of the rotor, wherein the rotor and the stator are arranged so that the front end of one of the magnetic poles of the stator aligns with a circumferential center of one of the permanent magnets of one of the magnet groups when the front end of the other of the magnetic poles of the stator aligns with a circumferential end of one of the permanent magnets of the other of the magnet groups.  
     
     
       13. A motor comprising: 
       a stator;  
       a solenoid unit for magnetizing the stator when energized;  
       a rotor having a rotor core disposed rotatably relative to the stator and a plurality of permanent magnets arranged on a circumferential periphery of the rotor core; and  
       a magnetic member covering the permanent magnets,  
       wherein the permanent magnets are divided into a pair of magnet groups separated from each other in a circumferential direction leaving spaces therebetween, the permanent magnets are arranged in at least partial contact with a circumferentially adjacent one in each of the magnet groups, and the permanent magnets are magnetized in a same direction in each group and in an opposite direction from that in the other of the magnet groups, wherein the magnetic member has non-magnetic parts which cover the spaces, wherein the non-magnetic parts comprise slits in the magnetic member which face the spaces between the magnet groups.  
     
     
       14. A motor as in claim  13 , wherein each of the permanent magnets is in a flat plate or rod shape extending in an axial direction. 
     
     
       15. A motor as in claim  13 , wherein the magnetic member is in a cylindrical shape. 
     
     
       16. A motor as in claim  13 , wherein the magnetic member and the permanent magnets have a substantially uniform gap circumferentially therebetween. 
     
     
       17. A motor as in claim  13 , wherein each of the permanent magnets has a trapezoidal cross section and is arranged circumferentially to contact fully with a circumferentially adjacent permanent magnet. 
     
     
       18. A motor as in claim  13 , wherein each said permanent magnet is magnetized in a radial direction. 
     
     
       19. A motor as in claim  13 , wherein spaces between adjacent two of said permanent magnets in each magnet group are filled with a non-magnetic material and said magnetic member comprises a resin material mixed with fine magnetic particles molded to an outer periphery of said magnet groups. 
     
     
       20. A motor as in claim  13 , wherein the magnet groups are arranged symmetrically with respect to the rotary axis of the rotor. 
     
     
       21. A motor as in claim  13 , wherein the stator is coupled with a solenoid unit for providing a pair of magnetic poles which face the magnetic poles of the rotor when the solenoid unit is energized, the magnetic poles of the stator having respective front ends that the magnet groups first approach during rotation of the rotor and wherein the front ends of the stator are arranged asymmetrically with respect to the rotary axis of the rotor. 
     
     
       22. A motor comprising: 
       a stator;  
       a solenoid unit for magnetizing the stator when energized;  
       a rotor having a rotor core disposed rotatably relative to the stator and a plurality of permanent magnets arranged on a circumferential periphery of the rotor core; and  
       a magnetic member covering the permanent magnets, wherein the permanent magnets are divided into a pair of magnet groups separated from each other in a circumferential direction leaving spaces therebetween, and the magnetic member has non-magnetic parts which cover the spaces, wherein said non-magnetic parts comprise slits in the magnetic member which face the spaces between the magnet groups.  
     
     
       23. A motor comprising: 
       a stator;  
       a solenoid unit for magnetizing the stator when energized;  
       a rotor having a rotor core disposed rotatably relative to the stator and a plurality of permanent magnets arranged on a circumferential periphery of the rotor core, said permanent magnets being arranged in two groups having spaces therebetween; and  
       a magnetic member covering the permanent magnets, said magnetic member having slits defining non-magnetic parts of the magnetic member that are disposed solely above said spaces between said permanent magnet groups, wherein the magnetic member and the permanent magnets have a substantially uniform gap circumferentially therebetween.  
     
     
       24. A motor as in claim  23 , wherein each said slit extends in an axial direction of the rotor core and the magnetic member includes cylindrical covering parts covering the magnet groups and connecting parts that connect the covering parts at axial ends of the slits. 
     
     
       25. A motor comprising: 
       a rotor having a pair of magnet groups thereon for providing a pair of magnetic poles respectively around a rotary axis thereof, each of the magnet groups including a plurality of permanent magnets arranged in a circumferential direction;  
       a solenoid unit; and  
       a stator coupled with the solenoid unit for providing a pair of magnetic poles which face the magnetic poles of the rotor when the solenoid unit is energized, the magnetic poles of the stator having respective front ends that the magnet groups approach first during rotation of the rotor,  
       wherein one of (1) the front ends of the stator and (2) the magnet groups are arranged asymmetrically with respect to the rotary axis of the rotor, whereby the front ends of the stator are asymmetrical relative to the magnets of the rotor with respect to the axis of rotation, thereby to reduce periodic fluctuations in generated torque arising from said front ends during rotation of the rotor, wherein one of the front ends of the stator is displaced in the circumferential direction from a diametrical line crossing the rotary axis of the rotor and the other of the front ends of the stator, wherein a diametrical line crossing the rotary axis of the rotor and a circumferential center of one of the magnetic groups crosses a circumferential center of the other of the magnet groups.  
     
     
       26. A motor comprising: 
       a rotor having a pair of magnet groups thereon for providing a pair of magnetic poles respectively around a rotary axis thereof, each of the magnet groups including a plurality of permanent magnets arranged in a circumferential direction;  
       a solenoid unit; and  
       a stator coupled with the solenoid unit for providing a pair of magnetic poles which face the magnetic poles of the rotor when the solenoid unit is energized, the magnetic poles of the stator having respective front ends that the magnet groups approach first during rotation of the rotor,  
       wherein one of (1) the front ends of the stator and (2) the magnet groups are arranged asymmetrically with respect to the rotary axis of the rotor, whereby the front ends of the stator are asymmetrical relative to the magnets of the rotor with respect to the axis of rotation, thereby to reduce periodic fluctuations in generated torque arising from said front ends during rotation of the rotor,  
       wherein the rotor has a magnetic member covering the magnet groups, and  
       wherein the magnet groups are separated from each other in the circumferential direction leaving spaces therebetween, and the magnetic member has non-magnetic parts which cover the spaces, wherein said non-magnetic parts comprise slits in the magnetic member.